1. Field of the Invention
The invention relates to an electrical power breaker having erosion-resistant contact members and a insulating nozzle.
2. Discussion of Background
Electrical power breakers are known which have a power current path with two contact members which can move relative to one another. During disconnection, an arc occurs in the switching path between the two contact members, part of which burns in an insulating nozzle. The thermal effects of the arc act on the surface of the insulating nozzle, and the nozzle constriction, which is critical to the flow conditions in the insulating nozzle, burns out, so that the cross section of the nozzle constriction is enlarged. If this increase in cross section exceeds certain limits, it has a negative influence on the disconnection capacity of the power breaker. In order to keep this undesirable increase in cross section comparatively small, erosion-resistant fluorocarbon polymers, for example polytetrafluoroethylene (PTFE), are used for the production of the insulating nozzle. These fluorocarbon polymers on the one hand have relatively low shape erosion, but on the other hand have comparatively high local depth erosion, which extends into the deeper regions under the surface of the insulating nozzle. Particularly as a result of the depth erosion, carbon is released which causes undesirable sooting of the insulating nozzle erosion channels, which are located under the surface. These sooted surfaces of the erosion channels which, in consequence, are electrically conductive, can, once the arc has been extinguished, lead to restrikes between the two power breaker contact members, which are then at a different potential, and this can lead to failure of the power breaker.
In order to avoid damaging sooting, an appropriate filler or a pigment can be added to the respective fluorocarbon polymer. Such additives largely prevent, in particular, depth erosion and thus the sooting but, as a rule, they result in a greater erosion rate and thus greater depth erosion as well, so that the life of the insulating nozzle is greatly reduced. This means that the insulating nozzle must be replaced comparatively frequently in the course of time-consuming maintenance of the power breaker.